The present invention relates to an improved printable film having good ink adhesive properties and relates more particularly to an improved printable film having good adhesive properties when used with radiation curable ink.
In recent years, diversification of printed products has required printing on a wider variety of materials in sheets; for example, papers, synthetic papers, polymer films such as thermoplastic resin films, metallic foils, metallized sheets, etc. These printed items are printed by methods such as by offset printing, gravure, flexography, screen process printing and letterpress printing. In these printing methods, a method which uses radiation curable ink has recently become popular because radiation curable inks cure rapidly, and the printing method which uses radiation curable ink is of superior handling. Radiation curable inks are known to be useful in the printing of packaging, labels and non absorbing printing materials. Radiation curable printing inks typically contain unsaturated acrylates, polyesters, photoinitiators, and additives. In electron beam cured inks however, the photoinitiators may be omitted.
After deposition of the radiation curable ink on the printable item, the print is exposed to radiation and hardens within a fraction of a second. Printing speeds up to 300 m/min are attained during continuous printing. At present, there is a great demand for sheet-like printable items.
In printing methods, the printing sheet requires sheet running properties anti-blocking properties, producing uniform spread of the ink over the surface of the sheet, as well as antistatic properties. Besides these generally required properties, in printing methods which use radiation curable ink, the printing sheet requires in particular the property of adhering strongly to radiation cured ink.
In particular, radiation curable ink printed polymer films, intended for use as labels, for example in the bottle labelling market, should be resistant to both freezing water conditions (i.e. storage in coolers or ice buckets for 24 hours) and boiling water conditions (i.e. pasteurization by immersion in water at 95° C. for up to 1 hour).
European patent application EP-A1-410051 discloses printing sheets comprising a support layer and a surface layer on at least one face of said support, said surface layer containing at least an acrylate based polymer and an unsaturated compound (cinamic acid or derivatives thereof).
Neither this document, nor any other documents of the state of the art do teach anything about the possibility of use of other monomers to replace cinamic acid.
However, the above listed materials formed in sheets, especially polymer films do not sufficiently adhere to radiation curable ink after printing and curing, especially in these extreme conditions. Accordingly the printed and radiation cured ink has a problem in the fact that the printed and radiation cured ink separates from the polymer film.
Therefore, a printable film which has superior adhesion to the radiation curable ink, even in extreme conditions, is required.